Field of the Invention:
The invention relates to a thyristor circuit including a transformer having a primary winding connected to an electric circuit and a secondary winding connected to a bipolar thyristor switch.
Such thyristor circuits, in various embodiments, can serve directly or indirectly, i.e., by inductive coupling, as switchable or short-circuitable inductances in an ac circuit, e.g., as switchable chokes in a reactive compensator or also, provided with suitable additional components, as variable power supply devices, which draw a regulated dc voltage from an ac circuit.
A thyristor circuit as above noted is known (U.S. Pat. No. 4,173,039), and is designed as a variable power supply device, with a primary winding, placed between two primary connections, through which an alternating current flows, and two secondary windings inductively closely coupled both with the primary winding and with one another, the first of which is parallel to a bipolar thyristor switch which is controlled a firing pulse generator, and a second of which charges a capacitor by a full-wave rectifier. A regulating circuit triggers the firing pulse generator as soon as the voltage on the capacitor exceeds a preset value. The first secondary winding is then short-circuited by the thyristor switch. Thereupon, the second secondary winding, because of the close inductive coupling with the first winding, delivers no further charging current.
Such thyristor circuits are subject to the limitation that the amount of the current flowing between the primary connections must be in a range which is limited upward by the fact that the current flowing through the thyristor switch must not exceed the maximum forward voltage of the switch, and is limited downward by the fact that it must reach at least the latching current of the thyristor switch at the firing times. When these limits are exceeded either upward or downward, the thyristor switch is threatened with destruction or not firing, with possibly fatal consequences. With power supply devices, for example, exceeding of the maximum allowable output voltage and destruction of the connected devices can result.
This results in a limitation in regard to the range in which the primary current can vary, which excludes the usual thyristor circuits from certain applications.
The object of this invention is to provide a novel thyristor circut, in which the admissible range of variation of the primary current is expanded in comparison with known thyristor circuits.
This object, and others, are achieved according to the invention by providing a novel thyristor circuit including a transformer having plural inductively coupled windings, wherein a first winding is provided with two primary connections for connection to an electric circuit, and at least a first bipolar thyristor switch which is placed between two connections of a second winding. The thyristor circuit further includes at least a second bipolar thyristor switch which is placed between two other connections of the second winding, wherein the number (N.sub.2) of windings between the connection between which the second bipolar thyristor switch is placed, is in each case smaller than the number (N.sub.1) of windings between the connections, between which the first bipolar thyristor switch, or immediately preceding bipolar switch in the case of more than two such switches, is placed.
The advantages obtained by the invention are especially to be seen in that it provides thyristor circuts whose range of application is substantially expanded in comparison with usual thyristor circuits. Many problems are amenable in general only to the thyristor circuits according to the invention, e.g., dc voltage supply from a high-voltage line with occasionally greatly varying power supply.